Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$78.33	12.662%	$88.2481	$88.25	$88.25	$88.20
Purchase #2	$196.66	9.394%	$215.1342	$215.13	$215.15	$215.10
Purchase #3	$49.49	5.230%	$52.0783	$52.08	$52.10	$52.10
Purchase #4	$136.51	11.692%	$152.4707	$152.47	$152.45	$152.50
Purchase #5	$137.66	4.572%	$143.9538	$143.95	$143.95	$144.00
Purchase #6	$148.74	3.145%	$153.4179	$153.42	$153.40	$153.40
Purchase #7	$146.46	13.656%	$166.4606	$166.46	$166.45	$166.50
7 purchase totals =	$893.85		$971.7636	$971.76	$971.75	$971.80